Introducing a Novel In Vitro Model to Characterize Hydrodynamic Effects of Percutaneous Nephrolithotomy Systems

Purpose: To widen the understanding of the fluid mechanics during percutaneous nephrolithotomy (PCNL), a new in vitro model for empiric studies was developed. Our first aim was to characterize common PCNL systems with regard to their intrapyelocaliceal pressure and their irrigation flow volume as possible parameters of hydrodynamic invasiveness. Materials and Methods: The model is based on a watertight cylindrical cast. Low pressure miniaturized PCNL (miniPCNL) systems and conventional PCNL systems were tested. Intrapelvic pressure and the total of irrigation flow volume per minute were measured for each PCNL system at 10 predefined levels of irrigation pressure between 40 and 130cm H2O. Results: Linear regression showed a linear relation between irrigation pressure and intrapelvic pressure. Compared with miniPCNL systems, conventional PCNL sheaths with closed Rutner sidearm generate significantly higher intrapelvic pressures. Opening the Rutner sidearm leads to a decrease in intrapelvic pressure to the level of the open mini PCNL systems. Polynomal regression revealed a square root relation between irrigation pressure and irrigation flow volume. Conclusions: Our in vitro model is suitable for obtaining reliable and valid data of intrapelvic pressure and irrigation flow volume of commonly used PCNL systems. Conventional PCNL sheaths with opened Rutner sidearm provide intrapelvic pressure and irrigation volume similar to miniPCNL. Consequently, a relevant difference of the hydrodynamic impact between conventional and miniPCNL systems are not necessarily to be assumed. Regression analysis revealed a new starting point for further empiric research of fluid mechanics during PCNL.